The “Hinge Zone” is the area where the Brunt Ice Shelf, which is mostly flat and floating on the water, is attached to the continental ice sheet, which sits on a bedrock and follows its curvature.
The Brunt Ice Shelf is formed by the continental ice sheet which is moving downhill toward the sea (2 meters a day) and hence originally has an inclination angle. When in starts to be supported by sea water, it “wants” to lay flat and is influenced by tidal effects.
The ice sheet, albeit very thick (about 200m) cracks at this particular point but all the fissures and crevasses are eventually covered by snow and freeze solid again, forming the flat and horizontal Brunt Ice Shelf which goes on for miles and miles.
This is this zone of temporary (from a geological point of view) turmoil is what we call the Hinge Zone. It is also the area with the most important relief and gives good opportunities for ice climbing and caving.